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Prolactin receptor antagonists that inhibit the growth of breast cancer cell lines
1Department of Protein Engineering, Genentech, Inc., South San Francisco, California 94080, USA.
Abstract:
We investigated the mechanism of action of the human prolactin (hPRL) receptor on four different breast cancer cell lines, T-47D, MCF-7, BT-474, and SK-BR3, that express elevated levels of the receptor compared with normal cells. Cells treated with human growth hormone (hGH), which binds and activates the hPRL receptor, exhibited bell-shaped dose-response growth curves consistent with the sequential dimerization mechanism proposed for the hPRL receptor (Fuh, G., Colosi, P., Wood, W.I., and Wells, J.A. (1993) J. Biol. Chem. 268, 5376-5381). Growth stimulation was enhanced by Zn2+, which preferentially increases the affinity of hGH for the hPRL receptor. Furthermore, receptor-selective variants of hGH that bind the hPRL receptor but not the hGH receptor were agonistic, providing additional support that specific binding to the hPRL receptor can stimulate these breast cancer cells to grow. On this basis we produced variants of hGH and human placental lactogen (hPL) that were potential antagonists because they bind but do not dimerize the hPRL receptor. The hPL-based antagonist was less potent than the hGH-based antagonist toward the growth of MCF-7 cells, consistent with the lower affinity of hPL for hPRL receptor than for hGH. However, the hPL-based antagonist was more potent than the hGH antagonist for BT-474 cells. Antibodies to the hPRL receptor inhibited growth of FDC-P1 cells transfected with the hPRL receptor; these also inhibited MCF-7 cells and T47D cells but not BT-474 cells. A unique feature of BT-474 cells was found when screening its cDNA revealed the presence of a novel alternative splice of the hPRL receptor that codes for the soluble extracellular domain; this may explain these differential inhibitory effects. These studies provide further molecular insight into the potential role of the hPRL receptor in breast cancer and demonstrate that hPRL receptor antagonists can inhibit the growth of breast cancer cells.
Insights
This study reveals that human prolactin (hPRL) receptor antagonists can inhibit breast cancer cell growth. Researchers identified a novel hPRL receptor splice variant in BT-474 cells, explaining differential responses to treatments.
Area of Science:
- Endocrinology
- Molecular Biology
- Oncology
Background:
- The human prolactin (hPRL) receptor is implicated in breast cancer growth.
- Understanding its mechanism of action is crucial for developing targeted therapies.
Purpose of the Study:
- To investigate the mechanism of action of the hPRL receptor in breast cancer cell lines.
- To evaluate the potential of hPRL receptor antagonists in inhibiting breast cancer cell proliferation.
Main Methods:
- Utilized four breast cancer cell lines (T-47D, MCF-7, BT-474, SK-BR3) expressing elevated hPRL receptors.
- Administered human growth hormone (hGH) and its variants, human placental lactogen (hPL), and antibodies targeting the hPRL receptor.
- Analyzed cell growth responses and receptor binding affinities.
- Screened cDNA for novel splice variants of the hPRL receptor.
Main Results:
- hPRL receptor activation by hGH promoted cell growth, consistent with a sequential dimerization mechanism.
- Growth stimulation was enhanced by Zn2+ and specific hGH variants acting as agonists.
- Developed hPRL receptor antagonists (hGH- and hPL-based) inhibited cancer cell growth.
- A novel alternative splice variant of the hPRL receptor was identified in BT-474 cells, potentially explaining differential responses to antagonists and antibodies.
Conclusions:
- The hPRL receptor plays a significant role in breast cancer cell proliferation.
- hPRL receptor antagonists demonstrate potential as therapeutic agents for breast cancer.
- A novel soluble extracellular domain splice variant of the hPRL receptor influences cellular response to therapeutic interventions.